If you know where the oil dipstick is, the transmission dipstick is very similar but closer to the firewall. Engine must be idleing to check tranny. There are normally marks on the stick that read "cold" and "hot". That describes the level of fluid dependant on tranny temp. Transmission fluid should be changed around every 30,000 miles. Symptoms of bad tranny, assuming good clean fluid, are hard shifting, won't shift (i.e.stays in 2nd gear) Or you accelerate and the tranny spins then jerks the car suddenly. An honest tranmission shop can tell.

Well in the 99 isuzu amigio there isnt a dip stick becaused its a sealed transmission... best to just take it to a dealership

The 10-minute oil change/other fluid Mobil shop where I bring my vehicles was able to do the fluid change for just over a $100. As Zoso0885 had stated two years back, the ****** stick/pan is a self contained unit under the Amigo held in by four bolts. From what I've read, if it's not leaking and you know the last time it was checked then it should be OK, otherwise just pony up the $100 and have it changed.